Research On High Temperature Superconducting Terahertz Detector

Terahertz (THz) radiation covers the frequency range from 10" Hz to 1013 Hz. Comparing with its counterparts in other frequency bands, THz wave has many special advantages which can be widely used in various areas, such as materials science, physics, chemistry, biology, medicine, non-destructive testing, astronomy, communications, military, etc. Due to lack of effective generation and detection techniques, the development of THz technology has been extremely slow in the early stages. Therefore, the research on highly sensitive THz detector are still the key factor in THz science and technology.High temperature superconductor (HTS) Josephson junctions have good response to THz waves. THz detectors of Josephson junctions have the advantages of high sensitivity, low noise and large bandwidth. HTS YBa2Cu3O7-d (YBCO) grain boundary bicrystal Josephson junctions can be employed as THz detectors. They can be operated at different working modes based on different principles. This paper aims at fundamental research and practical applications of HTS YBCO grain boundary Josephson junction terahertz detectors. The main contents are described as follows:1) The YBCO grain boundary junction is used to detect the THz emission from the HTS BSCCO emitter.7 Shapiro steps in the YBCO junction are induced. The numerical calculation based on RCSJ model shows that, the THz emission power detected by YBCO detector is ～82 μW at 500 GHz. This can be considered as the first step towards an integrated HTS THz receiver.2) A fast THz detection method is developed using the YBCO grain boundary junction, when the THz signal under detection is with modest intensity. The intensity and the frequency can be measured directly by reading the current reduction and the position of the induced first order Shapiro step. This method has been successfully used to evaluate the emission properties of the HTS BSCCO emitter.3) A prototype HTS THz spectrometer based on Hilbert transform has been built. The frequency range is from 0.1 THz to 2.5 THz and the best resolution is about 0.04 GHz@ 114 GHz and 2 GHz@ 1.78 THz.4) Two practically useful THz harmonic mixer systems have been developed, of which one is bulky, suitable for lab research and the other rather compact, for practical measurement. These two systems are both tested by a VDI THz source with the power of 20μW at 623 GHz. Shapiro steps and up to the 200th harmonic mixings are observed clearly.